Repeated experiments have clearly indicated that infection of specific pathogen free chickens with Marek's disease herpesvirus (MDV) leads to atherosclerosis. The viral induced arterial lesions closely resemble chronic human atherosclerotic lesions both in character and distribution. Studies in progress or planned concern the possible viral mechanisms involved which lead to atherosclerosis. These will include comparative in vitro and in vivo studies on the nature of MDV injury to arterial cells. Studies are also planned to determine whether inoculation of birds with avirulent herpesvirus strains will have any effect on development of arterial lesions in birds infected with virulent MDV.